1. Field of the Invention
The present invention relates to apparatus, method and computer program product for performing improved image formation in, for example, a laser printer, digital copying machine, etc.
2. Discussion of the Background
With respect to methods for forming an image in a digital copying machine, there is generally known a negative/positive (N/P) process in which laser light is radiated on a position corresponding to a black portion of manuscript data. The image is formed by putting toner on a radiated area. Since a diameter of the laser light beam is usually larger than a theoretical size of a single dot (i.e., with respect to dots per inch (DPI)), in the N/P process when the image is formed on a portion where the laser light is radiated (i.e., the image portion area), a black line of a single dot width is usually reproduced thicker than the theoretical single dot width. Although this results in a continuous reproduced line, the reproduced line, however, is thicker than the width of the theoretical single dot.
Accordingly, since the reproduced single dot black line becomes thicker than the black line of the manuscript document and the white single dot line becomes thinner, there arises a problem that the reproducibility may be worsened. In particular, in the case of the so-called grandson copying of re-using the copied sheet as the manuscript document, the phenomenon thereof appearing at that time may become further prominent.
Furthermore, as the troublesome matter of forming the electrophotographic image, there is a difference in the reproducibility of the lengthwise line and the transverse line. In general, the lengthwise line is reproduced thickly than the transverse line. Therefore, when the image forming condition is determined, the transverse line is apt to be made thinner than the manuscript document at the time of fitting to the lengthwise line. In contrast, the lengthwise line is apt to be made thicker than the manuscript document at the time of fitting to the transverse line. Those are the troublesome matters to be solved. That results in the difficulty of deciding the image forming condition.
In such the situation, as the background art of solving the troublesome matters, for instance, the published specification of Japanese Laid-open Patent Publication No. 5-75816 discloses the technology of preventing the ruin (destruction) of the non-image part on the single dot line and thereby improving the reproducing property by determining the density of the target pixel and the more than two pixels immediately adjacent thereto for the binary-value image data. Furthermore, the published specification of Japanese Laid-open Patent Publication No. 6-89338 discloses the technology of determining the print starting position of the target pixel on a basis of the relationship between the target pixel and the pixels adjacent thereto for the multiple-value image and putting the target pixel close to the adjacent pixels and printing the image in such the state, and thereby the reproducibility of the fine line and the edge portion of the image can be improved.
However, according to the technology disclosed in Japanese Laid-open Patent Publication No. 5-75816, since the reproducibility of the single dot line can be improved by compensating the density only for the binary image data, there arises the other problems (troublesome matters to be solved) that the edge portion of the line extending over the plural pixels for the multi-value image and the single dot line of the black color become too thick, or, in contrast, the single dot line of the white color is destroyed (the aforementioned phenomenon of the ruin or destruction). In addition, the thickness of the lengthwise line and the transverse line become different from each other. Those matters are also the problems to be solved.
Furthermore, according to the technology disclosed in Japanese Laid-open Patent Publication No. 6-89338, only it is possible to improve the reproducibility of the fine lines divided into two or more pixels and the edge portion of the image. However, the compensation of the line width is not taken into consideration when the thickness of the lengthwise line and the transverse line differ from each other. Those matters are also the problems to be solved.
Moreover, in both of the above-mentioned technologies, it was impossible to select whether or not the compensation is performed or not performed in consideration of the unevenness between the machines in accordance with the image pattern.